To meet current emission regulations, automotive vehicles must have on-board diagnostic systems to detect the malfunction of any component of the emission system, including a catalytic converter. A vehicle containing more than one catalytic converter may monitor each catalytic converter to guarantee detection of degraded system performance. An example would be that of a vehicle containing a V-type engine where catalytic converters coupled near or close to the engine are used. In this system, each catalytic converter may be monitored to determine emission compliance.
Catalytic converter monitoring systems are known in which an upstream and a downstream exhaust gas oxygen sensor are compared to give an indication of catalytic degradation. If sufficient degradation occurs, these systems will diagnose the deteriorated performance and illuminate a malfunction indicator. As a result, a new catalytic converter will be required. In the example of a V-type engine using two close coupled catalytic converters, each being monitored, when the measured performance of either of the two catalytic converters falls below a predetermined threshold, a malfunction is indicated. An example of such an approach is disclosed in U.S. Pat. No. 5,357,751.
The inventors herein have recognized numerous problems with the above approach. For example, in systems containing a dual bank engine connected to two monitored catalytic converters, the catalytic converters may not age at the same rate. Thus, one catalytic converter may have degraded past a threshold indicating possible reduced performance while the other is operating with much higher performance. While the total emissions of the vehicle are still within allowable amounts, a malfunction is indicated because one of the catalytic converters has degraded much faster than the other.